Most of the currently utilized predictive biomarkers for therapeutic decision-making provide information about the presence or absence of the drug target, but reveal little about the functional circuitry of the signaling network that the drug must also impact. Ex vivo biomarkers are dynamic molecular markers evoked from living tumor cells after removal from the patient. Such ex vivo biomarkers provide valuable mechanistic information that may facilitate drug development and guide the clinical selection of targeted therapeutics. We propose to develop a companion diagnostic test, named SnapMap, for drugs targeting the ErbB signal transduction network. This test will utilize tumor biopsy samples processed on the SnapPath[unreadable] tumor processing system to evoke ex vivo biomarkers from live tumor samples.